1. Field of the Invention
The present invention concerns a material with high energy per mass unit (E.sub.g) providing a high specific impulse (I.sub.s). This material could be used in particular as rocket fuel. The invention also provides a process for producing such a material. Specifically, a high energy complex of metastable helium fixed on ammonia is addressed.
2. Background of the Prior Art
The most widely used propellant at present is formed by a mixture of liquid hydrogen and oxygen which releases an energy of E.sub.g =32 kcal/g, providing a specific impulse I.sub.s =528 sec. This propellant is considered as having the highest energy among those currently used, its ejection speed being 5180 m/sec.
In order to save costs, a continued need is felt for a propellant releasing considerably higher energy than the known liquid hydrogen and oxygen propellant both because distant space missions (because of the better payload to propellant weight ratio) requires such a fuel and also because then single stage to orbit vehicles might become feasible.
The physical-chemical reactions releasing the highest energy are (Schmidt, "Technische Thermodynamik", Springer 1963; Peschka "Proceedings of the IX international astronautical congress" Amsterdam 1958; Rosen, "Current status of free radicals and electronically excited metastable species as high propellants" Drexel University, Philadelphia Pa.):
First the recombination of atomic hydrogen: EQU H+H=H.sub.2 +4.3 eV
102.8 kcal/mol=51.4 kcal/g=4.3 eV giving I.sub.s =2100 sec and an ejection speed of 20770 m/sec.
Second the recombination of metastable Helium: EQU (2.sup.3 S.sub.1) He.sub.m =(1S.sub.o) He+19.82 eV (a)
(theoretical lifetime 8200 sec) EQU (2.sup.1 S.sub.o) He.sub.m =(1S.sub.o) He+20.61 eV (b)
(theoretical lifetime 0.02 sec)
(Because of the considerably shorter lifetime reaction (b) is not important and will not be considered below.
444 kcal/mol=111.2 kcal/g=19.82 eV; giving I.sub.s =3100 sec and an ejection speed of 30000 m/sec.
Neither of these reactions is possible when the electron spins (.vertline.) are aligned in parallel. In fact, according to Heitler-London (Weitzel, "Lehrbuch der Theoretischen Physik", Springer 1958, Berlin--Gottingen--Heidelberg)--only hydrogen atoms with antiparallel spins recombine to form a hydrogen molecule (H.sub.2) and--according to the Pauli--principle (Weitzel, above ref.)--the two He - electrons in their basic state (both in the "K"-shell) must have antiparallel spins. In the metastable state one electron is in the "K"-shell and the other in the "L"-shell and as long their spins are kept parallel recombination is impossible because of forebidden transfer. This parallel spin alignment is well known and offers a possibility to keep an electron in the "L"-shell.
It was thought (Peschka, see above ref.) that the parallel alignment of electron spins could be obtained by means of application of an external magnetic field at low temperature to reduce the tendency of thermal disturbance as much as possible. Since that time extensive and thorough experimental and theoretical research has been conducted on atomic hydrogen and the following has been established:
(a) atomic hydrogen may be maintained stable for hours at densities varying between 10.sup.16 and 10.sup.17 atoms/cm.sup.3 (magnetic field 5 Tesla, temperature lower than 1.degree. K.). PA1 (b) the parallel alignment of the two electron spins is possible to secure by means of a magnetic field.
The practical application of these results, however, does not seem possible in the near future.
Insofar as metastable He is concerned, the inventors have no knowledge of the existence of research carried out in this field. The disadvantage of both reactions--atomic hydrogen and metastable helium--is that for the parallel aligned electrons nearly no activation energy is required to assume antiparallel spin; even in a strong magnetic field at low temperature saturation is only asymptotically achieved which means that there is always a finite number of electrons changing from parallel to antiparallel spin and will recombine. The heat released will then ignite via chain reaction the metastable species in case they were stored in higher concentrations or densities--which of course should always be the case for the application concerned.
It should be emphasized, however, at the same time that atomic hydrogen and metastable helium behave chemically in the same way as alkaline metals because they have also only one electron in the outer shell. (Muschlitz Jr. "Metastable atoms and molecules", Science Vol. 159, February 1968).